1. Field of the Invention
This invention relates to pumping molten metal and more particular to an improved coupling assembly connection between a drive and an impeller in a molten metal pump.
2. Brief Description of Prior Art
A molten metal pump apparatus generally includes a motor mounted above a molten metal bath. The motor drives a rotatable impeller pump having one or more impellers submerged in the bath. In operation, the rotating impellers draw molten material from the bath and pump it through a conduit routed to a subsequent station for further processing. The impellers are coupled to one end of a vertically oriented impeller shaft. An opposite end of the impeller shaft extending above the molten metal bath is affixed to a female coupling member. In many pump apparatuses, the end portion of the impeller shaft is threaded. To secure the impeller shaft to the coupling member, the impeller shaft is screwed into a correspondingly internally threaded portion of the female coupling member. An end of the drive shaft extending from the motor is received in the coupling member and pinned thereto providing a mechanical linkage between the rotating motor drive shaft and the pump impellers.
Some prior art couplings transmit torsional forces between the shaft end and coupling by providing a “modified square” coupling arrangement formed in the socket. This “modified square” is sized to receive a complimentary shaft end configuration such that the two shapes are closely fitted together. This “modified square” configuration has been found unsatisfactory since the internal corner portions of the coupling can be placed in shear and can cause fracture and premature wear. In addition, the prior art configurations are difficult and time consuming to clean.
Desirably, a coupling assembly would be available that would enable the impeller to be easily connected and would have superior strength characteristics. In addition, advantageous features would include a drive motor-impeller shaft connection that would permit the shaft to connect and disconnect easily from the drive motor without requiring excessive handling or machining of the shaft. In addition, it would be desirable to have a drive motor-impeller shaft connection that would be stronger than conventional shaft connections or the prior art “modified square” design. It would also be advantageous to have a coupling that can easily be cleaned in a very short period of time. The coupling assembly of the present invention satisfies these advantages.